How Does the Automatic Control of Breathing Adjust to Life’s Demands?

          Almost all cars now come equipped with cruise control.  This handy piece of automation allows you to set a desired speed for your car and then enjoy a foot-free ride as you cruise down the highway. If you begin to slow down as you climb up a hill, a feedback signal is sent to a control unit, and the system adjusts by opening the throttle, allowing more air and fuel into the engine until the set speed is reached again.  Maintaining a particular speed is one less thing you have to think about while driving. The only problem is having to brake because a car in front of you slows down. The newer “adaptive cruise controls” have come to the rescue, as they add another level of automation.  Radar and camera systems have been installed to monitor the distance of the cars in front of you, automatically reducing the speed when that distance is too close.  When the distance increases, the car automatically speeds up until it reaches the speed you have set. With this feature you can really “cruise” down the highway!

It’s pretty obvious that the minds of the some of the best engineers have been and will continue to be busy imagining and designing these automated systems which make the job of driving easier.  How does this relate to breathing? The Engineer of our body has made automatic breathing controls “standard equipment” for all models!  These controls, located in the brain stem, can automatically adjust our speed of breathing to whatever we’re doing at the moment, so that we can really “cruise” down the highways and byways of life in style. (not just “foot-free”, but also “thought-free”!)

          I like to think of the brain as a “prisoner - king”.   He is a king because nothing takes place in our body unless he directs it (like scratching your nose when it itches)  He is a prisoner because he’s trapped in a completely dark tower with no direct connection to the outside world. So, how can a king rule wisely when he himself is cut off from the world around him?  The king we call our brain relies on faithful messengers (nerves) to relay information to him from within and without of the body so he can decide what to do. The part of our brain we’re aware of, in which we do our thinking, is the cerebral cortex.  It makes up the top layers of our brain.  Tucked down below it is the brain stem, which we’re not aware of.  Though not under conscious control, the decisions it makes are the difference between life and death, as it controls things like our breathing, swallowing, heart rate, blood pressure, consciousness, and sleep. 

          If you saw the respiratory centers in the brain stem you wouldn’t be impressed.  Yet, those tiny clumps of tissue are keeping us alive right now.  One clump controls all aspects of the inhalation process (breathing in).  Somehow it uses a built-in timer to fire a message down the phrenic nerve connected to the diaphragm, signaling for it to contract every two seconds, which brings air into the lungs. This is followed by a relaxation period of another two seconds during which time we exhale (breath out).   These messages (contract/ relax) are repeated every 4 seconds over 20,000 times each day without our ever giving it a second thought.  You can sleep in perfect peace, knowing your respiratory control center will continue its work of bringing the breath of life into your lungs.   If we need to breathe out with more force a separate cluster of cells in the medulla of the brain stem fire nerve messages to contract stomach and rib muscles to push air out faster.  Our breathing is smooth and perfectly coordinated because of the precise directions from this group of control centers.  The best thing about them is that we’re totally free to live our lives without ever having to give breathing another thought.

           But, just like a car we do not live life at one speed.  What happens when we climb a mountain, play basketball, soccer or ultimate frisbee?  Did you know that intense physical exercise can increase breathing rates from 12-18 time per minute up to 40-50 times per minute? (1)  During strenuous exercise we can burn up to eight times more oxygen than when we’re resting.  Why?   More muscle power requires burning more muscle fuel (ATP).  Making more ATP’s means using more oxygen to convert more glucose into ATP. (see # 2: “Solving the Problem of Why We Need to Breathe” for more on this) We can only get more oxygen by taking deeper breaths and breathing faster. 

          But, wait.   Did you think about needing to breathe faster when you started chasing the soccer ball down the field? No, that’s the last thing you need to be worried about in the middle of a soccer game.   If it wasn’t you, then who told your diaphragm and rib muscles they needed to work faster?  Or does your respiratory control center have an “adaptive cruise control” that will automatically adjust your breathing rate to your circumstances?  Yes, and it goes way beyond the car version in automation.  We would call the car version “semi-automatic”, as it relies on input from the driver.  When the speed limit changes, the driver must again input a new speed into the system. In order to be fully automatic our respiratory center must know at any given moment what our body’s oxygen needs are, and then be able to set a new breathing speed to meet that demand without us having to think about it at all.

          The correct ratio of air to fuel in automobile engines is 14.7 parts air to 1 part fuel.  This ratio of air to fuel, controlled by the powertrain control module (PCM), must constantly be monitored and adjusted to insure that the fuel burns cleanly so that fuel is not wasted and our atmosphere is not polluted with carbon emissions.  The PCM relies on feedback from an oxygen sensor installed in the exhaust pipe.

This sensor compares the amount of oxygen in the exhaust with levels in outside air and then produces a voltage reading which is sent to the PCM.  If no oxygen is present in the exhaust a high voltage is generated. When this message is received by the PCM it automatically reduces fuel input into the engine (too rich). If there is high oxygen present in exhaust a low voltage is generated, which the PCM interprets as “too lean”, and increases the fuel input into the engine.  This automatic control center (PCM) and its oxygen sensor is called a closed feedback loop, as input received from its built-in sensor allows the control module to adjust the air-fuel ratio to produce the best engine results. Each part of this system has been designed by engineers to “respond” appropriately under different conditions to produce optimum performance of the engine.    See  https://www.youtube.com/watch?v=-JOyjuBwaBE.

In part 2 we’ll see how our built-in breathing control system has its own feedback loop, providing a fully automatic delivery of oxygen to our cells, and you can be the judge in deciding if this coordinated system could have come about by chance.

Endnotes:

1.. https://www.ptdirect.com/training-design/anatomy-and-physiology/acute-respiratory-responses